1. Field of the Invention
This disclosure relates to an image forming apparatus that transfers a toner image carried on an image carrier onto a recording medium.
2. Description of the Related Art
There is known an image forming apparatus configured to form a toner image carried on a rotating endless belt-like intermediate transfer member (hereinafter, referred to as an intermediate transfer belt) and transfer the toner image onto a recording medium at a transfer nip portion at which a rotating transfer member (transfer belt or transfer roller) is in contact with the intermediate transfer belt. In order to transfer the toner image onto the recording medium from the intermediate transfer belt, a high voltage is applied to the rotating transfer member and thus, a high electric field is produced at the transfer nip portion. The recording medium is guided to the transfer nip portion along the intermediate transfer belt by a conveyer guide.
The intermediate transfer belt vibrates during rotation in some cases. When the intermediate transfer belt vibrates, a gap may be formed between a toner image carrying surface of the intermediate transfer belt and the recording medium at upstream of the transfer nip portion (upstream side of the intermediate transfer belt in a rotating direction). As described above, since the high electric field is produced at the transfer nip portion, an abnormal electrical discharge may occur between the intermediate transfer belt and the recording medium in a case where the gap is formed upstream of the transfer nip portion. When the abnormal electrical discharge occurs, a charge of the toner carried on the intermediate transfer belt is lost and the toner which has lost charge is not transferred onto the recording medium from the intermediate transfer belt. Then, an image defect (referred to as a void, a white space, or the like) like an empty white portion is caused at a position where an abnormal electrical discharge occurs. Therefore, as disclosed in JP-A-2002-82543, an apparatus is proposed, in which a pushing member is provided on an inner circumferential side (back surface side opposite to a toner image carrying surface) of an intermediate transfer belt, pushes the intermediate transfer belt from the back surface, and stretches the belt to a rotating transfer member side, and thereby vibration of the intermediate transfer belt which causes an abnormal electrical discharge is suppressed.
However, when the intermediate transfer belt is greatly stretched by the pushing member, a recording medium guided by a conveyer guide becomes closer to the intermediate transfer belt. In such a case, when the recording medium is, particularly, cardboard, coated paper, or the like, which has high bending stiffness, the recording medium collides with the intermediate transfer belt on the upstream side from the pushing member in a rotating direction of the intermediate transfer belt and the recording medium is bent and thus, the recording medium and the intermediate transfer belt strongly rub against each other. When the recording medium and the intermediate transfer belt strongly rub against each other, an unfixed toner image carried on the intermediate transfer belt is disturbed. As a result, an image defect referred to as “deterioration of graininess” or the like appears on the recording medium after transferring.